In recent usage, filtering membranes are widely used in daily life for removing impurities in water. The filtering membranes are usually a porous polymer membrane having tiny pores. Solid impurities are intercepted by the tiny pores when a liquid passes through, amid therefore only a purified liquid can pass through the filtering membrane. For example, water filtered by a reverse-osmosis membrane or a nano-sized membrane can be used directly as drinking water or pure water for industrial use.
In typical applications, either the reverse-osmosis membrane or the nano-sized membrane is formed of a plurality layers with a dense-selective layer coated on their surface. The dense-selective layer is usually formed by interface polymerization. In practice, a filtering membrane having a high interception ratio and a high flux can usually meet the user's requirements, no matter what fields the filtering membrane would be used in. Conventional methods for improving the characteristics of the filtering membrane include modifying the surface of the filtering membrane or adding hydrophilic inorganic addition agents (e.g., nanoparticles or nanotubes) to the filtering membrane. However, the modifying process is complicated and difficult to control. The inorganic addition agents are difficult to disperse uniformly in the filtering membrane because the inorganic addition agents are formed of inorganic materials and the filtering membrane is formed of organic polymers.
Thus, a novel addition agent which can effectively improve the flux and the retention ratio of a filtering membrane is needed.